FM Tute M01 QGIS 1D2D Links

Introduction

In this section we will create the 1D/2D links to join the Flood Modeller 1D component to the TUFLOW 2D domain.
As described on the previous page, this consists of a boundary line with type "HX" and a series of connection lines that connect the 1D computation points to the HX line.
The HS line is how flow is transfered between the 2D TUFLOW domain and the 1D Flood Modeller Domain.
For this tutorial the HX lines and a sample of the "CN" lines have been provided.

The empty GIS files used in this tutorial are the same as those created in step 4 of tutorial module 1.
These template files set up how to enter the GIS data for TUFLOW to read.

Method

1. Import in an empty 2d_bc_empty_L.shp layer from within the FMT_tutorial\FMT_M01\TUFLOW\model\gis\empty folder.
2. Save the empty layer as 2d_bc_FMT_M01_HX_001_L.shp in the FMT_tutorial\FMT_M01\TUFLOW\model\gis folder.
3. Open the 1D_2D_HX_Links_L.shp GIS layer from Module_Data\Module_01\gis folder. Select all objects from within this layer, copy and paste into 2d_bc_FMT_M01_HX_001_L.shp.
4. Interrogate one of the lines running along the banks of the watercourse. These lines are the 1D/2D boundary links and have been assigned a type ‘HX’.
5. Interrogate one of the lines connecting the x1D node to the HX line. These are the connection or ‘CN’ lines that read the water level from Flood Modeller and transfers this to the HX line.
In the figure below, the water level is calculated in Flood Modeller at the nodes FC01.16, FC01.15 and FC01.14. These water levels are linearly interpolated along the lengths of the HX line on both left and right banks of the watercourse. When the water level exceeds the elevation of the boundary cell, water is able to flow on the the TUFLOW 2D floodplain.


Note that where there are junctions within the Flood Modeller 1D model (i.e. at structures), both the upstream and downstream nodes are connected to TUFLOW. Refer to the below figure, the Junction nodes are highlighted in red and the upstream and downstream nodes are highlighted in green.
The HX lines must be broken between the nodes. This is a requirement of a linked Flood Modeller – TUFLOW model. In the figure below, the HX lines are broken between FC01.35 and FC01.34 as a culvert is located between these nodes.
900px
6. The CN and HX lines between nodes FC02.06 and FC02.01d along the tributary have not been digitised. Digitise these lines to connect the nodes to the 2D domain.
   To digitise the CN lines, make the 2d_bc_FMT_M01_HX_001_L.shp layer editable. For each node in the 1d_x1d_FMT_M01_nodes_001_P.shp layer, draw a line in your GIS pack from the node to the HX line. The line must snap to both the node and the HX line. Draw two lines for each node, one to the left bank and one to the right bank. In the 'Type' attribute of each line, type 'CN'.
   
   The figure below shows how the nodes are connected at the confluence. Note that all Flood Modeller nodes at the junction are present within the 1d_x1D_nodes layer, and are connected to the 2D domain. The HX lines are broken around the junction.


7. Once all the CN and HX lines have been digitised along the tributary, save the file.

Key Tip!

The digitised direction of the HX and CN lines is not important. The CN lines however should be digitised approximately perpendicular to the direction of flow. Two CN lines are digitised for each node and connected to the HX boundary lines along the left and right banks. The HX boundary lines should be digitised along the top of each bank such that the width between the lines approximately correlates to the width of the 1D channel.

Please return to the Flood Modeller Tutorial Model.